1. Field of the Invention
The invention relates to the field of phosphine-based catalysts. More particularly, it relates to new phosphine-based ligands that are useful in preparing catalysts that show improved performance in the telomerization of butadiene.
2. Background of the Art
It is generally known that 1-octene may be efficiently prepared via the telomerization of butadiene. This telomerization is typically done in the presence of methanol, and the catalyst is frequently a combination of a Group VIII metal, such as palladium, and a known phosphine ligand. The telomerization is frequently a three-step process. In the first step, butadiene is telomerized together with methanol to yield 1-methoxy-2,7-octadiene (“MOD-1”). In the second step, MOD-1 is hydrogenated to yield methyloctylether. In step three, the methyloctylether undergoes ether cleavage to yield 1-octene and methanol.
One known method of accomplishing the telomerization step uses a catalyst that is a combination of a palladium salt and triphenylphosphine (TPP). However, less than desirable yields of 1-octene are encountered when using this phosphine. This appears to be due, at least in part, to side reactions that lead to formation of 3-methoxy-1,7-octadiene (“MOD-3”) and 1,3,7-octatriene.
Another approach is disclosed in U.S. Pat. No. 7,425,658, which teaches a method for producing 1-octene from butadiene by dimerizing and alkoxylating butadiene in the presence of one or more alkoxy-substituted phosphine ligands. This is done under alkoxydimerization conditions with an alkoxydimerization catalyst. Illustrative phosphine ligands include tris(2,4,6-trimethoxyphenyl)phosphine and tris-(4-methoxyphenyl)phosphine.
Co-pending International Application No. PCT/US09/051,347, filed on Jul. 22, 2009, teaches telomerization of 1,3-butadiene in the presence of an organic hydroxyl compound, a palladium (Pd) catalyst and at least one of a group of novel phosphine ligands. Illustrative phosphine ligands include tris-(2-methoxyphenyl) phosphine, tris-(2,4-dimethoxy-phenyl)phosphine, bis-(2-methoxyphenyl)phenylphosphine, tris-(2-methoxy-4-fluorophenyl)-phosphine and tris-(2-methoxy-4-chlorophenyl)phosphine.
U.S. Pat. No. 7,026,523 discloses a method for telomerizing non-cyclic olefins that includes use of a Pd-carbene complex as a catalyst.
Unfortunately, none of the known methods appears to satisfactorily achieve the goals of increased levels of catalytic activity and yield, combined with reductions of undesired side products. Because of this, producers of 1-octene via the butadiene telomerization route continue to search for new catalysts that offer improvements in any or all of these goals. The present invention addresses this need.